Inductance coils are commonly used in various electrical, electronic and electromechanical applications. It is well known that the electrical characteristics of an inductance coil are dependent on the size and shape (e.g. the number of coil turns) of the coil, as well as a number of other factors. In practice, inductance coils are designed with a particular purpose in mind, and as a consequence, it is a basic design requirement that an inductance coil maintain its original electrical characteristics during its service life. This, in turn, implies that the inductance coil maintain its original shape (i.e. does not deform or fracture in service).
In use, inductance coils generate magnetic fields which are proportional in strength to the current that is passed through the coil. These magnetic fields, in turn, generate magnetic forces, the strength of which are proportional to the square of the magnitude of the magnetic fields. When relatively high currents are passed through single layer inductance coils, strong magnetic forces are generated that can deform the coil.
During high current flow, wires in single layer solenoid inductors are exposed to significant magnetic forces. Relative to a circular coil, these forces comprise or include two primary components. The first component is oriented perpendicular to the axis of the coil and produces a hoop stress in the wire. This hoop stress results from the magnetic pressure that is generated by the relatively high field inside the coil and the relatively low field outside the coil. In addition, there is a “turn to turn” force on the wires that causes the wires next to each other to be pulled together. This “turn to turn” force is most pronounced on the ends of the coil and causes the wires on the end of the coil to try to move toward the center of the coil. The forces balance near the center of the inductor and these axial forces are less of a concern at the center of the coil. On the other hand, because the forces are strong near the coil ends, the termination of the coil ends must withstand relatively strong forces.
The above-described axial forces can also cause unrestrained cyclic deformations (which are typically more pronounced when pulsed currents are used) that can lead to fatigue failure and result in a relatively short inductor service life. In addition, another factor that must be considered is the heating (i.e. ohmic heating) that occurs during current flow through the inductor. Prior art devices in which the coil is completely embedded in a dielectric structure (e.g. fiberglass) are prone to overheating. Overheating of the inductance coil can alter the electrical characteristics of an inductance coil and decrease fatigue cycles to failure. Although the problem of overheating may be overcome by using a hollow, tubular conductor as an inductor coil and passing a cooling fluid therethrough, this solution is overly complicated and typically requires cooling lines, pumps and controllers.
In light of the above, it is an object of the present invention to provide an inductor that has a relatively long service life when used with relatively high currents that are repetitively pulsed. It is another object of the present invention to provide a high pulsed current inductor which maintains a suitable service temperature and does not overheat in use. Yet another object of the present invention is to provide a high pulsed current inductor and a method for manufacturing a high pulsed current inductor which are easy to use, relatively simple to implement, and comparatively cost effective.